86 Secundianus of Thambei said: "We ought not to deceive heretics by our too great forwardness, that not having been baptized in the Church of our Lord Jesus Christ, and having therefore not received remission of their sins, they may not impute to us, when the day of judgment comes, that we have been the cause of their not being baptized, and not having obtained the indulgence of the grace of God. On which account, since there is one Church and one baptism, when they are converted to us, let them receive together with the Church the baptism also of the Church."
87. Nay, when they are transferred to the rock, and joined to the society of the Dove, let them receive the remission of their sins, which they could not have outside the rock and outside the Dove, whether they were openly without, like the heretics, or apparently within, like the abandoned Catholics; of whom, however, it is clear that they both have and confer baptism without remission of sins, when even from themselves it is received by men, who, being not changed for the better, honor God with their lips, while their heart is far from Him. Yet it is true that there is one baptism, just as there is one Dove, though those who are not in the one communion of the Dove may yet have baptism in common.
Source: On Baptism, Against the Donatists (New Advent)